1. Field of the Invention
The present invention generally relates to power converters, and, more specifically, the present invention relates to boost power converters.
2. Description of the Related Art
FIG. 1 shows a conventional PFC (power factor correction) power converter, which is embodied in boost topology. The PFC power converter comprises a bridge rectifier 10, a magnetic device 15, a controller 90, a power switch 20, a rectifier 40, a capacitor 50, a line resistor 35, a current-sensing resistor 25, and a voltage divider. The controller 90 comprises a line terminal LN, an output terminal SW, a feedback terminal FB, a sensing terminal VN, and a ground terminal GND. The bridge rectifier 10 rectifies an AC line voltage VAC into an input voltage VIN. The magnetic device 15, which is an inductor for example, is connected between an output of the bridge rectifier 10 and an anode of the rectifier 40. A first terminal of the power switch 20 is connected to the anode of the rectifier 40. A second terminal of the power switch 20 is connected to a ground reference. The line resistor 35 is coupled to detect the input voltage VIN for providing an input-voltage signal IAC to the line terminal LN of the controller 90. The capacitor 50 is connected between a cathode of the rectifier 40 and the ground reference. The controller 90 generates a switching signal SW via its output terminal SW to a control terminal of the power switch 20 for generating an output voltage VO, which is obtained across the capacitor 50. The voltage divider formed by resistors 71 and 72 is connected in parallel with the capacitor 50. A joint of the resistors 71 and 72 provides a feedback signal VFB, which is proportional to the output voltage VO, to the feedback terminal FB of the controller 90. The current-sensing resistor 25 is connected between the second terminal of the power switch 20 and the sensing terminal VN of the controller 90. Referring to FIG. 1, as the power switch 20 is turned on, a switching current IL of the magnetic device 15 will be equal to a charging current IW flowing via the power switch 20 and return to the bridge rectifier 10 via the current-sensing resistor 25 (charging path). As the power switch 20 is turned off, since the polarity of the magnetic device 15 reverses, the switching current IL will be equal to a discharging current IDS flowing via the rectifier 40 and return to the bridge rectifier 10 via the current-sensing resistor 25 (discharging path). The current-sensing resistor 25 is coupled to sense the switching current IL of the magnetic device 15. Since the current-sensing resistor 25 is connected via both the charging path and the discharging path of the magnetic device 15, the switching current IL sensed by the current-sensing resistor 25 can be calculated as a switching current average. As a result, the technique used in the circuit schematic of FIG. 1 is the well known “average-current control technique”. However, the drawback of PFC power converters utilizing this technique is higher power consumption across the current-sensing resistor 25. Furthermore, these PFC power converters also fail to be connected in parallel to achieve higher efficiency, such as the solution shown in an U.S. Pat. No. 7,626,372 titled “Control Circuit for Multi-phase, Multi-channels PFC Converter with Variable Switching Frequency”.